JP5022999B2 - Powder magnetic core and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnetic core such as a smoothing choke coil used in a switching power supply and the like, and a method for manufacturing the same.

  With the increase in performance and functionality of various electronic devices, currents have increased, and soft magnetic materials used for magnetic cores such as choke coils used in such electronic devices have characteristics that have small characteristic changes even at large currents, that is, excellent DC superimposition and low loss are required.

Ferrite cores and dust cores are used as choke coils used at high frequencies. Among these, the ferrite core has a defect that the saturation magnetic flux density is small. On the other hand, a dust core produced by molding metal alloy powder has a higher saturation magnetic flux density than soft magnetic ferrite, and thus has excellent DC superposition characteristics.

  As this metal alloy powder, Sendust, which is an alloy of silicon, aluminum, and iron, Permalloy, which is an alloy of nickel and iron, silicon steel, which is an alloy of silicon and iron, and the like are used. Further, the use of an amorphous alloy, which is an amorphous soft magnetic alloy, has been studied as a lower loss alloy.

In order to produce a powder magnetic core using these amorphous alloy powders, a method is known in which a metal alloy powder is mixed with a low-melting glass and an organic binder, compression- molded at high pressure, and then heat-treated. Yes.

For example, the prior art, as in Patent Document 1, a method of performing high-density molding an at mold and the powder in the high temperature, as in Patent Document 2, such as a metal alloy powder low-melting glass and an organic binder There is a method of mixing and molding at high pressure at room temperature.

  However, in the methods of Patent Document 1 and Patent Document 2, a low-melting glass powder is fixed on the surface of the amorphous soft magnetic alloy powder, which is higher than the softening point of the glass and higher than the crystallization temperature of the amorphous soft magnetic alloy powder. However, the pressure is formed at a low temperature, and the apparatus is expensive and the process is complicated, so that it is not suitable for mass production.

  Furthermore, although the method of patent document 1 and patent document 2 can obtain a low-loss powder magnetic core, since the pressurization density of a powder magnetic core is not enough, it cannot acquire the outstanding DC superposition characteristic. . Therefore, in order to improve the direct current superimposition, which is a problem, it is necessary to increase the density of the dust core, but in reality, it is impossible to increase the density of the dust core.

Therefore, as in Patent Document 3, 30-60 wt% amorphous alloy powder and 70-40 wt% pure iron powder are used at a low pressure of 5 ton / cm ² for the purpose of improving the DC weight characteristics. Using a magnetic alloy powder having two different particle sizes, as in the method of forming, or Patent Document 4, even if the forming pressure is low, the powder having a small particle size fills the gap to increase the forming density. A method for improving the characteristics of the magnetic core has been proposed.

Further, as in Patent Document 5, one of the powders having different average particle diameters is subjected to insulation treatment, and thereafter, using a method such as hot pressing, plasma discharge sintering, hot isostatic pressing (HIP) or the like. A method has been proposed in which the molding temperature is 400 to 500 ° C. and the molding pressure is 200 to 600 MPa.

JP-A-10-212503 JP 2001-73062 A JP 07-34183 A JP 2006-176817 A JP2007-220876

  However, although the method of Patent Document 3 seems to improve direct current superimposition by mixing pure iron into fine powder in addition to amorphous soft magnetic alloy powder, it is a low frequency at high frequency, which is the original purpose. I can't expect a loss.

  In addition, in the method of Patent Document 4, in order to obtain a magnetic alloy powder having a small particle diameter, a soft magnetic alloy is subjected to an embrittlement treatment in a hydrogen atmosphere, and then the embrittled soft alloy is treated. Smash. However, this method is not suitable for mass production because the process becomes complicated. In addition, the pulverization causes distortion in the fine powder and causes an increase in hysteresis loss.

Furthermore, the method of Patent Document 5, when the room temperature to normal press forming, can not itself be molded because no binder resin, to do molding, hot pressing, a plasma discharge sintering and heat A method such as hot isostatic pressing (HIP) is required. However, such a method causes problems such as molding speed and cost. Although the use of a spark sintering method is also conceivable, in the spark sintering method, it is necessary to insulate one of two kinds of powders having different average particle diameters and to insulate one of them. For this reason, problems such as an increase in eddy current loss due to the non-insulating powder occur.

As described above, a powder magnetic core made of amorphous soft magnetic alloy powder has a problem in terms of mass production due to its poor formability compared to other metals despite its excellent magnetic properties. Further, since the powder itself is hard, a sufficient density cannot be obtained even if the pressure during molding is increased, and excellent direct current characteristics cannot be obtained.

The object of the present invention is to solve the above problems and provide a powder magnetic core and a method for producing a powder magnetic core that have excellent direct current characteristics and magnetic characteristics even when low pressure molding is performed at room temperature, as in the case of conventional metal alloys. There is to do.

Based on the above-mentioned object, the dust core of the present invention, only the binder resin as two or more of the composite magnetic material powder and a binder uniformly dispersed amorphous soft magnetic alloy powder is mixed, pressure molding Then, in the powder magnetic core formed by annealing the molded body, the composite magnetic material powder is a first amorphous soft magnetic alloy powder having an average particle size of 30 to 100 μm, and The first amorphous soft magnetic alloy powder is made of a second amorphous soft magnetic alloy powder having a mean particle size of 1 to 15 μm smaller than the first amorphous soft magnetic alloy powder. It is processed at a temperature lower than the crystallization temperature of the amorphous soft magnetic alloy, the surface of the composite magnetic material powder is coated with a silane coupling agent as a heat-resistant protective film, and the binding resin is Methylphenyl silicone resin or average particle size is 1 It is characterized by being a polypropylene powder or polyethylene powder of ˜15 μm. According to the above configuration, by mixing two types of amorphous soft magnetic alloy powders having different particle sizes, it is possible to obtain excellent direct current superimposition and magnetic characteristics even when low-pressure molding is performed at room temperature. In addition, it is possible to reduce costs by using an amorphous soft magnetic alloy powder produced by a water atomization method as the second powder.

In the present invention, since the surface of the composite magnetic material powder is coated with a silane coupling agent as a heat resistant protective film, heat treatment is performed in the atmosphere by using the silane coupling agent as a heat resistant protective film. Even when it is performed, iron loss can be reduced without lowering the magnetic permeability than when the silane coupling agent is not used. Therefore, it is possible to reduce the iron loss by using the silane coupling agent even if the amount of the binder resin is small.

Furthermore, in the present invention, the binder resin is a methylphenyl-based silicone resin or a polypropylene powder or polyethylene powder having an average particle diameter of 1 to 15 μm. Therefore, when heat treatment is performed in an oxidizing atmosphere (in the air), The methylphenyl silicone resin or the polypropylene powder or polyethylene powder having an average particle diameter of 1 to 15 μm remains on the surface of the amorphous soft magnetic alloy powder and becomes a strong binder and insulating film. In particular, in the methylphenyl silicone resin, the methyl group directly bonded to the Si group is thermally decomposed at 350 ° C., and then silica (SiO 2 ₂ As a layer, since this is a strong silica film, the insulating property does not deteriorate even when heat treatment is performed at high temperature in the atmosphere, and the influence of an increase in hysteresis loss due to oxidation or the like can be reduced.

Another aspect of the present invention is characterized in that the added amount of the second amorphous soft magnetic alloy powder is 5 to 30 wt%. That is, within this range, the maximum magnetic flux density and magnetic permeability can be maintained high, but when it is more than this range, the maximum magnetic flux density and magnetic permeability are reduced.

  In another aspect of the present invention, the applied magnetic field H = 20 kA / m, the maximum magnetic flux density is 600 mT or more, and the powder magnetic core according to any one of claims 1 to 4 is characterized.

Two or more kinds of amorphous soft magnetic alloy powders having different average particle diameters as described above are mixed, and the surface is coated with an inorganic insulating material, press- molded , and heat-treated to provide excellent direct current superposition characteristics. A manufacturing method for obtaining a dust core is also an embodiment of the present invention.

According to the present invention as described above, two or more kinds of amorphous soft magnetic alloy powders having different average particle diameters are mixed, the surface is coated with an inorganic insulating material, press- molded , and heat-treated. It is possible to provide a dust core excellent in direct current superposition characteristics with loss and a method for manufacturing a dust core.

The manufacturing method of the powder magnetic core of the present embodiment includes the following steps.
(1) A mixing step of mixing a composite magnetic material powder in which two or more kinds of amorphous soft magnetic alloy powders having different average particle diameters are uniformly dispersed and a binder resin.
(2) A coating step of coating the composite soft magnetic powder and the binding resin with methylphenyl silicone resin, polypropylene powder or polyethylene powder.
(3) forming step of preparing a methylphenyl-based silicone resin or polypropylene powder or soft magnetic powder and a binder resin coating the polyethylene powder, pressure molding process to the molded body.
(4) annealing of the molded body is annealed passed through the molding process.
Hereafter, each process is demonstrated concretely.

(1) Mixing step In the mixing step of the present embodiment, 85 wt% of the first powder having an average particle size of 45 μm and 15 wt% of the second powder having an average particle size of 4 to 12 μm having different particle sizes are mixed with a mixer (balls). Mix for 24 hours using an unused pot mill).

(2) Coating step In order to coat the mixture that has undergone the mixing step with a binding tree, 0.1 wt% of a silane coupling agent is coated on the mixture and dried at room temperature for 24 hours. Next, 1.0 wt% of methylphenyl silicone resin is mixed and dried at 180 ° C. for 2 hours. Furthermore, 0.2 wt% of zinc stearate is mixed as a lubricant.

Methylphenyl silicone resin used in the coating step of the present embodiment, after the high solvent resin concentration has evaporated has a sticky feel, in the heating and drying of about 200 ° C. as described above optimally act as a binder during the molding . The addition amount of methylphenyl silicone resin is an appropriate amount of 0.5 to 2.0 wt%. If it is less than this, the strength of the molded body will be insufficient and cracks will occur. On the other hand, if the amount is more than 2.0 wt%, there arises a problem that the maximum density reduction due to density reduction and the magnetic characteristics due to an increase in hysteresis loss are deteriorated.

In the coating step of this embodiment, polypropylene powder or polyethylene powder may be used as a binder instead of methylphenyl silicone resin. At this time, the addition amount of polypropylene powder or polyethylene powder is suitably 1.0 to 3.0 wt%. If it is less than this, the strength of the molded body will be insufficient and cracks will occur. On the other hand, if it exceeds 3.0 wt%, there arises a problem that the maximum magnetic flux density is reduced due to the density reduction and the magnetic characteristics are lowered due to the increase in hysteresis loss. The average particle size of the powder is preferably equal to or less than the average particle size of the second powder soft magnetic alloy powder. If it is larger than this, the density will be reduced.

  Moreover, the silane coupling agent is mixed and coated on the soft magnetic alloy powder in order to form a heat-resistant protective film on the surface of the soft magnetic alloy powder, rather than a method that does not use the coupling agent. Hysteresis loss can be significantly reduced, and iron loss can be reduced. The silane coupling agent having good compatibility with the methylphenyl silicone resin is an amino silane coupling agent, and γ-aminopropyloxysilane is particularly preferable. Examples of the silane coupling agent having good compatibility with polypropylene powder or polyethylene powder are vinyl-based silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane. A methacryloxy silane coupling agent may also be used.

  Furthermore, in the coating step of this embodiment, by using zinc stearate, which is a metal salt of stearic acid, as a lubricant, it becomes possible to increase the thermal decomposition rate of methyl groups depending on the type of metal, even from a lower temperature. A strong silica layer is formed.

(3) Molding process
In the molding step, the soft magnetic alloy coated with the binder as described above is pressure- molded at a molding pressure of 1300 MPa at room temperature to form a molded body. Here, the pressure-dried methylphenyl silicone resin acts as a binder during molding .

(4) Annealing process In an annealing process, a powder magnetic core is produced by performing an annealing process with respect to the said molded object at 480 degreeC. Here, the heat treatment is performed at 480 ° C. at a temperature equal to or lower than the crystallization temperature of the amorphous soft magnetic alloy powder, while maintaining a certain degree of crushing strength. This is to prevent the iron loss from increasing due to the deterioration of the eddy current loss and the eddy current loss.

  In addition, when the methylphenyl silicone resin is heated to about 350 ° C. during the annealing treatment, the methyl group directly bonded to the Si group is thermally decomposed. Actually, the heat treatment of the dust core is carried out in the air, resulting in a dense and strong silica film. Therefore, even if heat treatment is performed at a high temperature, the insulation does not deteriorate and the hysteresis loss due to oxidation does not increase. . Furthermore, since the thermally decomposed methyl group does not remain as carbon by this heat treatment in the atmosphere, the mechanical strength can be improved.

Next, Examples 1 to 12 of the present invention will be described below with reference to FIGS. 1 to 5 and Tables 1 to 3.
[1. Measurement item]
As measurement items, permeability, maximum magnetic flux density, and direct current superimposition are measured by the following method. The magnetic permeability was calculated from the inductance at 100 kHz and 0.5 V by applying a primary winding (20 turns) to the produced powder magnetic core and using an impedance analyzer.

  The maximum magnetic flux density is obtained by applying a primary winding (170 turns) and a secondary winding (20 turns) to a dust core, and using a BH analyzer (Iwatori Measurement Co., Ltd .: SY-8232) as a magnetic measurement instrument. The magnetic flux density at an applied magnetic field H = 20000 A / m was measured. In addition, direct current superimposition is performed by applying a primary winding (170 turns) to each dust core and using an LCR meter (HP: 4284A) capable of measuring inductance, capacitance, and resistance. The inductance at each DC bias at 5 V was measured, and the magnetic permeability was determined by calculation.

[2. First characteristic comparison (when silicone resin is used as binder)]
The sample used for the first characteristic comparison was prepared as follows. First, 85 wt% of the first powder having an average particle size of 45 μm and 15 wt% of the second powder having an average particle size of 4 to 12 μm having different particle sizes were mixed for 24 hours using a mixer (pot mill not using balls). . Then, 0.1 wt% of the silane coupling agent is coated and dried at room temperature for 24 hours.

Next, 1.0 wt% of methylphenyl silicone resin is mixed and dried at 180 ° C. for 2 hours. Furthermore, 0.2 wt% of zinc stearate was mixed as a lubricant. This was press- molded at a pressure of 1300 MPa at room temperature to produce a dust core. Then, an annealing treatment is performed on these dust cores for 30 minutes.

  The relationship between the first powder and the second powder in Table 1 is as follows. Comparative Example 1 is a comparative example in which the second powder is not added to the first powder. The content of the first powder having an average particle size of 45 μm is 100 wt%, and the content of the second powder is 0 wt. %. In Examples 1 to 3, the first powder having the same average particle diameter as in Comparative Example 1 is 45 μm, the second powder is changed in average particle diameter, and the content of the second powder is 15 wt%. It is the Example which was made to add so. In Example 1, the average particle size of the second powder is 4 μm, in Example 2, the average particle size is 6 μm, and in Example 3, the average particle size is 12 μm.

  The first powder used in this embodiment is not limited to an average particle size of 45 μm, and may have an average particle size in the range of 30 to 100 μm. If the average particle size is larger than this range, eddy currents may be used. On the other hand, if the average particle size is smaller than this range, the hysteresis loss due to density reduction increases.

Table 1 is a table showing the relationship between the first powder, the second powder, the silicone resin, the coupling agent, the relative density, the magnetic permeability, and the maximum magnetic flux density for Examples 1 to 3 and Comparative Example 1. is there. FIG. 1 is a graph showing magnetic permeability and DC superposition characteristics.

  As can be seen from Table 1, Examples 1 to 3 in which the second powder was mixed had a higher relative density than Comparative Example 1 in which the second powder was not mixed, and the permeability and maximum magnetic flux at 100 kHz. The density is increasing. From the comparison between Example 1 in which the average particle size of the second powder is 4 μm and Example 3 in which the average particle size of the second powder is 12 μm, the average particle size of the second powder to be added is increased. It can be seen that the relative density, permeability, and maximum magnetic flux density are reduced. Further, as shown in FIG. 1, the permeability with respect to the DC bias magnetic field is a comparative example in which the second powder is not mixed in Examples 1 to 3 in which the second powder is mixed when the DC bias current is 0 to 10,000 A / m. It can be seen that it is higher than 1.

From Examples 1 to 3 and Comparative Example 1, by adding the second powder having a smaller average particle diameter to the first powder, the gap between the first powder is filled with the second powder at the time of molding. It can be seen that the molding density increases. It has also been found that by the action of the second powder, a high-density powder magnetic core can be produced even when the pressure during molding is the same.

[3. Second characteristic comparison (when polyethylene powder or polypropylene powder is used as the binder)]
The sample used for the second characteristic comparison was prepared as follows. First, 85 wt% of the first powder having an average particle size of 38 to 45 μm, 15 wt% of the second powder having an average particle size of 6 μm having a different particle size, polyethylene powder that is an adhesive resin powder, or polypropylene powder having an average particle size of 5 μm Was mixed for 24 hours using a mixer (pot mill without balls). This is pressure- molded at a pressure of 1300 MPa at room temperature, and the molded body is annealed for 30 minutes.

  The relationship between the first powder and the second powder in Table 2 is as follows. Comparative Example 2 is a comparative example in which the second powder is not added to the first powder, the content of the first powder having an average particle size of 45 μm is 100 wt%, and the content of the second powder is 0 wt. %. In Examples 4 and 5, the first powder having the same average particle diameter as in Comparative Example 2 is 45 μm, the second powder is changed in average particle diameter, and the content of the second powder is 15 wt%. It is the Example which was made to add so. In Example 4, the average particle size of the second powder is 4 μm, and in Example 5, the average particle size is 6 μm.

  The relationship between the first powder and the second powder in Table 3 is as follows. Comparative Example 3 is a comparative example in which the second powder is not added to the first powder. The content of the first powder having an average particle size of 45 μm is 100 wt%, and the content of the second powder is 0 wt. %. Examples 6 to 10 are examples in which the second powder having an average particle size of 6 μm was added to the first powder having the same average particle size of 45 μm as that of Comparative Example 3 by changing the addition amount. .

  In Example 6, the content of the first powder is 95 wt%, the content of the second powder is 5 wt%, and in Example 7, the content of the first powder is 90 wt%, The content is 10 wt%, Example 8 has a first powder content of 85 wt%, and the second powder has a content of 15 wt%. Example 9 has a first powder content of 15 wt%. 80 wt%, the content of the second powder is 20 wt%, and in Example 10, the content of the first powder is 70 wt% and the content of the second powder is 30 wt%.

  Examples 11 and 12 are examples in which the average particle size of the first powder was changed with respect to Example 8 in which the content of the first powder and the content of the second powder were the same. In Example 11, the average particle size of the first powder is 42 μm, and in Example 12, the average particle size of the first powder is 38 μm.

  The first powder used in the present embodiment is not limited to an average particle size of 38, 42, and 45 μm, and may have an average particle size in the range of 30 to 100 μm. If it is larger, the eddy current loss increases. On the other hand, if the average particle size is smaller than this range, the hysteresis loss due to density reduction increases.

Table 2 is a table showing the relationship among the first powder, the second powder, the polyethylene powder, the relative density, the magnetic permeability, and the maximum magnetic flux density in Examples 6 to 12 and Comparative Example 3. FIG. 2 is a graph showing magnetic permeability and DC superposition characteristics.

  As can be seen from Table 2, in Examples 4 and 5 in which the second powder was mixed, the relative density was higher than in Comparative Example 2 in which the second powder was not mixed, and the magnetic permeability and the maximum magnetic flux density were increased. . The average particle size of the second powder is preferably between 1 and 15 μm, and from Example 1 where the average particle size of the second powder is 4 μm and the example where the average particle size of the second powder is 12 μm, It can be seen that when the average particle size of the second powder is increased, the relative density, permeability, and maximum magnetic flux density are reduced.

  Further, as shown in FIG. 2, the permeability with respect to the DC bias magnetic field is a comparative example 2 in which the second powder was mixed in Examples 4 and 5 where the second powder was mixed when the DC bias current was 0 to 10000 A / m. It turns out to be higher.

Table 3 is a table showing the relationship among the first powder, the second powder, the polypropylene powder, the relative density, the magnetic permeability, and the maximum magnetic flux density for Examples 6 to 12 and Comparative Example 3. FIG. 3 is a graph showing the magnetic permeability and DC superposition characteristics, and FIG. 4 is a graph showing the relationship between the added amount of the second powder and the maximum magnetic flux density.

  As can be seen from Table 3, by mixing 5 to 30 wt% of the second powder, the relative density, magnetic permeability, and maximum magnetic flux density can be increased even in a dust core to which polyethylene powder is added. Moreover, according to FIG. 4, the maximum magnetic flux density becomes maximum when the addition amount of the second powder is 15 to 20 wt%, and then decreases. Furthermore, according to FIG. 5, the relative density becomes maximum when it is 15 wt%, and the relative density does not increase even if the amount of the second powder added is increased thereafter.

  From the above, the amount of the second powder added is preferably between 5 and 30 wt%. If it exceeds this range, the magnetic permeability and the maximum magnetic flux density will decrease. Further, as shown in FIG. 3, the permeability with respect to the DC bias magnetic field is a comparative example in which the second powder is not mixed in Examples 6 to 10 in which the second powder is mixed when the DC bias current is 0 to 10,000 A / m. It can be seen that it is higher than 3.

The graph which showed the magnetic permeability and direct current superimposition characteristic of the dust core at the time of changing the average particle diameter of 2nd powder in the 1st characteristic comparison of the Example of this invention. The graph which showed the magnetic permeability and direct current superimposition characteristic of the dust core at the time of using the polypropylene powder as 2nd powder in the 2nd characteristic comparison of the Example of this invention. The graph which showed the magnetic permeability and direct current superimposition characteristic of the powder magnetic core at the time of using polyethylene powder as 2nd powder in the 2nd characteristic comparison of the Example of this invention. The graph which showed the addition amount and maximum magnetic flux density of the 2nd powder of a powder magnetic core at the time of using the polyethylene powder as a 2nd powder in the 2nd characteristic comparison of the Example of this invention. The graph which showed the addition amount and relative density of the 2nd powder of a powder magnetic core at the time of using the polyethylene powder as a 2nd powder in the 2nd characteristic comparison of the Example of this invention.

Claims (5)

Only two or more of the binder resin as a composite magnetic material powder and a binder uniformly dispersed amorphous soft magnetic alloy powder is mixed, a molded body prepared by pressure molding, annealing the molded article In the processed dust core,
The composite magnetic material powder includes a first amorphous soft magnetic alloy powder having an average particle size of 30 to 100 μm and a second amorphous particle having an average particle size of 1 to 15 μm smaller than the first amorphous soft magnetic alloy powder. Of amorphous soft magnetic alloy powder,
The molded body is annealed at a temperature lower than the crystallization temperature of the amorphous soft magnetic alloy,
The surface of the composite magnetic material powder is coated with a silane coupling agent as a heat-resistant protective film,
The powder magnetic core according to claim 1, wherein the binder resin is a methylphenyl silicone resin or a polypropylene powder or polyethylene powder having an average particle diameter of 1 to 15 μm.   The dust core according to claim 1, wherein the amount of the second amorphous soft magnetic alloy powder added is 5 to 30 wt%. The dust core according to claim 1 or 2 , wherein the maximum magnetic flux density is 600 mT or more at an applied magnetic field H = 20 kA / m. Only two or more of the binder resin as a composite magnetic material powder and a binder uniformly dispersed amorphous soft magnetic alloy powder is mixed, a molded body was prepared The mixture was then pressure-molded, molded In the manufacturing method of the dust core for annealing the molded body,
A first amorphous soft magnetic alloy powder having an average particle size of 30 to 100 μm and a second amorphous soft magnetic alloy having an average particle size of 1 to 15 μm smaller than the first amorphous soft magnetic alloy powder The composite magnetic material powder composed of powder and a binder resin are pressure-molded to produce a molded shape,
The surface of the composite magnetic material powder is coated with a silane coupling agent that is a heat-resistant protective film before pressure molding,
The binder resin is a methylphenyl silicone resin or a polypropylene powder or polyethylene powder having an average particle size of 1 to 15 μm,
A method for producing a powder magnetic core, comprising subjecting the compact after the pressure molding to an annealing treatment at a temperature lower than a crystallization temperature of the amorphous soft magnetic alloy. The method for producing a dust core according to claim 4 , wherein the amount of the second amorphous soft magnetic alloy powder added is 5 to 30 wt%.

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